1. Field of the Invention:
This invention relates in general to earth boring drill bits, and in particular to an improved drill bit nozzle for discharging drilling fluid against the bottom of the bore hole.
2. Description of the Prior Art:
The most common type of bit for drilling oil and gas wells has three rotatable and generally conical cutters. The cutters have teeth that disintegrate the earth's formations during drilling. Fluid is pumped down from the string and discharged from three outlets in the bit. The fluid cools the bit and circulates cuttings up the borehole to the surface of the earth.
One type of drilling fluid is a liquid slurry known as "mud" that often contains particulates such as abrasive sand particles. Nozzles formed of sintered tungsten carbide are mounted in the fluid outlets of the bit to reduce erosion. Each nozzle is a short cylinder with a converging axial bore. It is retained within the bore by a snap or retaining ring received within a groove formed in the drilling fluid passage.
While this type of nozzle is in widespread use, the high velocity discharge of mud and resulting turbulence around the bit tends to erode the steel retaining ring, particularly when the mud contains a large amount of abrasive material. Erosion also occurs when the bit is in the hole a relatively long time, when the bit is drilling in a soft formation, and when an exceptionally high nozzle velocity is used. If the retaining ring breaks or loosens, the nozzle is rapidly expelled from the passage. The passage outlet quickly erodes, and the cutting teeth will be damaged by contact with the nozzle in the borehole.
When exceptional erosion conditions exist, a shrouded nozzle has been used in the prior art. One known shrouded nozzle has an annular groove for receiving the snap ring. The portion of the nozzle downstream of this annular groove serves as a flange to protect the snap ring from turbulently flowing fluid around the exterior of the bit. A segment of this circular flange is removed to provide access to the retaining ring ends for installation.
While this shrouded nozzle is successful, there is a tendency for cracks to occur at the sharp corners within the groove. These cracks occur because the shroud is comprised entirely of tungsten carbide and formed by a pressing technique which induces such cracks. Another disadvantage of tungsten carbide drill bit nozzles in general is the expense of the material.